1. Field of the Invention
The invention is directed to a strip-shaped substrate made from a film comprising a number of units for producing chip carriers as well as an electronic module with such a chip carrier, an electronic device with a module of this type and a method for producing a substrate.
2. Discussion of the Related Art
A strip-shaped substrate from a film with a number of units for producing chip carriers has been disclosed, for example, in DE 20 2012 100 694 U1, which goes back to the applicant.
The chip carriers produced from the strip-shaped substrate are used for electronic modules such as RFID chips (radio frequency identification) for use in chip cards. RFID chip cards have memory chips, which can be read and written to in a contactless manner with the aid of an external RFID antenna with radio frequency identification and transponder for energy supply. Possible areas of application of such RFID chips are identity documents with biometric data (ID-card, passport), health cards, bank cards or public transport tickets.
RFID chips of this kind are produced by placing a plurality of semiconductor chips encapsulated respectively in a casting compound or moulding compound onto the strip-shaped substrate mentioned in the beginning. To this end the strip-shaped substrate mentioned in the beginning comprises a film with a number of units for producing chip carriers, wherein each unit comprises a chip island for fixing the semiconductor chip, electrodes for electrically connecting the semiconductor chip and through-openings for structuring the unit. The modules formed in this way, after being subjected to a functional test, are separated from the strip and integrated with the chip card.
Since the chip cards are flat, the modules, on the one hand, must not exceed an overall maximum thickness. On the other hand, the modules must be sufficiently stable in order to prevent the chips or chip carriers from becoming damaged which in consequence could negatively affect the function of the chip card.
Furthermore, in order to ensure perfect functioning of the chip card the casting compound encapsulating the chip needs to be well anchored. To this end the through-openings provided in the substrate form anchoring edges for the casting compound in which the semiconductor chips are to be encapsulated.
With the substrate known from DE 20 2012 100 694 U1 the anchoring edge is formed by a graduation, serving as an undercut. The undercut/graduation is produced by embossing the underside of the substrate. During encapsulation of the chip the undercut is filled with the casting compound, thereby achieving the desired anchoring effect. The prerequisite for a sufficient anchoring effect is a minimum film thickness, so that the undercut can be given a depth providing the free space required for receiving the casting compound. The minimum film thickness limits to minimum overall thickness of the electrical module, which for the known substrate can in practice not be reduced any further without negatively affecting the functional reliability of the chip carrier.